1. Field of the Invention
The present invention relates generally to semiconductor technology and, more particularly, to a semiconductor structure, e.g. a metal gate or a word line of a vertical-channel transistor, and a method for making the same.
2. Description of the Prior Art
As circuit integration increases, the need for greater uniformity and process control regarding layer thickness rises. Various technologies have been developed to deposit layers on substrates in a cost-effective manner, while maintaining control over the characteristics of the layer.
Selective deposition methods such as selective chemical vapor deposition (CVD) processes are known in the art. Selective deposition may be used to deposit materials on selected surfaces of structures in the manufacture of integrated circuits, and thus obviates the need for associated lithography, etching, and resist removal steps. Selective CVD processes are advantageous because they allow for self-alignment with respect to various structures, thus allowing for relatively tight design rules.
However, the prior art selective deposition methods still have some drawbacks. For example, the prior art selective deposition methods are often used to grow tungsten layer in a contact hole. Prior to the deposition or growth of the tungsten in the contact hole, a series of cleaning steps are required to ensure the silicon surface cleanness. If Reactive Ion Etching (RIE) damage layer exists on the bottom of the contact hole, the metal film formed by the selective CVD process does not grow because the RIE damage layer may work as an insulating film. Therefore, the RIE damage layer needs to be removed before growth of the metal film.
In addition, the prior art selective deposition methods are apparently not able to provide a selectively deposited layer such as tungsten layer, which is not only a conformal, ultra-thin (below 15 nm) film but structurally continuous, on a metallic, non-silicon base layer. Also, it is difficult to maintain sufficiently high selectivity between dielectric layer and metal base layer and to deposit such conformal, ultra-thin film at the same time.
In light of the above, there is a need in this industry to provide an improved semiconductor structure and method for making the same, where a conformal, ultra-thin film is desired and the conformal, ultra-thin film can be selectively deposited on a metallic, non-silicon base layer with high selectivity between dielectric layer and metal base layer. It is also desirable to provide a method for making such conformal, ultra-thin film with higher throughput.